1. Field of the Invention
The invention relates to marine steering systems and, more particularly, relates to a power assist steering system for a boat or other watercraft. Specifically, the invention relates to a steering system that incorporates an operator controlled helm and a separate hydraulic steering cylinder that is controlled by the helm in a master/slave fashion to steer the watercraft.
2. Discussion of the Related Art
In a conventional marine steering system, a watercraft such as a boat is steered by pivoting a rudder and/or outboard motor on the stern of the watercraft about a vertical steering axis upon steering actuation by an operator stationed at the helm. One typical steering system for a boat having a hull-mounted motor comprises a steering cable extending between the steering helm and the motor so that steering at the helm actuates the cable to pivot the motor about the steering axis. The cable typically comprises a push-pull cable having a reciprocatable inner core slidable in a protective, flexible outer sheath or housing. One end of the cable is connected to the steering helm, and the other end is connected to a tiller arm coupled to the motor or rudder. When the wheel is turned at the helm, the cable is actuated by a push-pull movement of the inner core, thereby pivoting the tiller arm. These systems work reasonably well on small boats, but the steering forces required for pivoting the tiller arm increase progressively with system size to the point that many larger boats can be steered manually only with great difficulty, if at all.
In order to reduce the forces required to steer a watercraft, it is well-known with marine outboard drives, particularly those employing large displacements, to employ a hydraulic power steering assist system for assisting the operator in steering the boat. The typical hydraulic power steering assist system includes a hydraulic cylinder that is connected to a tiller arm or other steered mechanism and that is energized in response to operator control to actuate the steered mechanism. Specifically, a helm-responsive controller is coupled to a hydraulic cylinder assembly that, in turn, is coupled to the steered mechanism, either directly or via an intervening push-pull cable. When the steering wheel is turned one way or the other, hydraulic fluid is pumped from the steering helm to one end or the other of the cylinder assembly to pivot the motor one way or the other.
A power steering assist system that is generally of the type described above is described in U.S. Pat. No. 5,603,279 (the ""279 patent). The system described in the ""279 patent comprises a hydraulic cylinder-piston assembly and a helm. The cylinder-piston assembly has a reciprocally mounted piston and first and second chambers in the cylinder on opposite sides of the piston. The steering cylinder has a balanced piston. In fact, as with most systems of this general type, a rod extends through both ends of the steering cylinder making for a longer assembly. The helm includes two separate cylinder assemblies that are divided into four separate internal chambers by a stepped flanged piston. One of the cylinder assemblies forms a master cylinder that is actuated directly by a control valve assembly under power supplied from the pressure source. The portion of the piston in this part of the assembly is stepped so as to form an unbalanced cylinder in the helm. The second cylinder assembly comprises a slave cylinder divided into third and fourth chambers by an annular flange on an extension of the piston. The third and fourth chambers are coupled to respective chambers of a steering cylinder. The control valve assembly is actuatable to regulate the flow of hydraulic fluid into and out of the second chamber to drive the piston and, thereby, vary the volumes of the third and fourth chambers and driving the steering piston one way or the other within the steering cylinder to effect a steering operation. The actuator of the valve assembly comprises a rotatable valve body that has first and second valves mounted in it. A rotatable input member (e.g., a steering shaft or extension thereof), actuable upon steering at the helm, is operably connected to the valve actuator. Thus, steering at the helm actuates the valve actuator to regulate the flow of pressurized hydraulic fluid through the cylinder, thereby driving the piston in one direction or the other depending upon the steering direction.
The system disclosed in the ""279 patent, while effective, exhibits several drawbacks and disadvantages. For instance, because its helm has four chambers and, in effect, two pistons, it requires a great many seals. The helm is also relatively large (both axially and radially). In fact, it is so large that it must be formed from a casting rather than machined components. It is therefore difficult to mount on the back of the dashes of many smaller boats. Several of the hydraulic fittings on the helm also are necessarily located on the periphery of the helm rather than on the rear end, rendering it difficult to access those fittings after the helm is installed behind the dash.
Moreover, in the system disclosed in the ""279 patent, only part of the system (namely, the first and second chambers of the helm) is pressurized directly by the pressure source. The remainder of the system (namely, the third and fourth chambers of the helm and both chambers of the steering cylinder) is pressurized indirectly via translation of the slave portion of the piston. Air in the lines of that portion of the system can lead to noticeable xe2x80x9cloosenessxe2x80x9d or play of the cylinders.
Many of the problems associated with the ""279 patent were addressed and overcome in co-pending and commonly assigned application Ser. No. 09/967,792 (the ""792 application), filed Sep. 28, 2001, now U.S. Pat. No. 6,524,147 The system disclosed in the ""792 application includes a hydraulically actuated unbalanced steering cylinder assembly, a pressure source, and a helm that is spaced from the steering wheel assembly, typically within the dash. The helm includes a helm cylinder having a slave chamber fluidically coupled to a second chamber in the steering cylinder, a high pressure port fluidically coupled to the outlet of the pressure source and to a first chamber in the steering cylinder, and a return port fluidically coupled to a vent. A helm piston is slidably mounted in the helm cylinder, and a control valve assembly is movable between at least first and second positions to alternatively couple a control chamber in the helm cylinder to the high pressure and return ports, respectively. The resultant system is considerably simpler and more compact than that disclosed in the ""279 patent. It also is pressurized directly by a single source and, therefore, does not exhibit the looseness experienced by some other systems. In fact, it is extremely well configured for use in a relatively small, single engine watercraft. However, it is not easily adaptable to a multiengine watercraft having a separate steering cylinder for each rudder. It also is not usable with watercrafts having multiple helms.
In accordance with a first aspect of the invention, a power steering assist system for a watercraft includes a hydraulically actuated steering cylinder assembly and a helm. The steering cylinder assembly is configured for connection to a steered mechanism of the watercraft. It includes a steering cylinder, a steering piston that is mounted in the steering cylinder to define first and second chambers on opposite sides thereof, and a rod that is affixed to the steering piston. Either rod or the steering cylinder is movable relative to the other and is configured for connection to the steered mechanism. The helm, which is spaced from the steering cylinder assembly, has high pressure, return, and metering ports formed therein. The high pressure port is coupled to a fluid pressure source, the return port is coupled to a reservoir, and the metering port is coupled to the second chamber of the steering cylinder. The helm includes a metering element having at least first and second ports, the second port being coupled to the metering port in the helm, and a control valve assembly that is coupled to the metering element and that is switchable between at least first and second states to alternatively couple the first port in the metering element to the high pressure and return ports of the helm, respectively, thereby alternatively permitting pressurized fluid to flow into the metering port from the metering element and from the metering port into the metering element. The control valve assembly may also be switchable to a third, neutral state in which the first port of the metering element is isolated from both of the high pressure and return ports.
In a preferred embodiment, the control valve assembly comprises first and second two-way/two-position valves that are configured to be actuated by an operator manipulated steering mechanism (such as steering wheel) such that 1) both the first and second valves remain closed when the steering mechanism remains stationary, 2) movement of the steering mechanism in a first direction opens the first valve while leaving the second valve closed, and 3) movement of the steering mechanism in a second direction opens the second valve while leaving the first valve closed. In this case the control valve assembly preferably comprises a valve actuator and a valve body, the valve body 1) being rotatably coupled to the metering element and to the steering mechanism, 2) housing the first and second valves, 3) having a first passage formed therein that couples the high pressure port to the first port of the metering element, and 4) having a second passage formed therein that couples the first port of the metering element to the return port. The valve actuator is movable relative to the valve body between first, second, and third positions thereof corresponding to the first, second, and third states of the valve assembly.
The system preferably additionally includes a relief valve assembly that allows the system to be operated manually in the event of pressure source failure. The relief valve assembly may include a two-way/two-position pilot-operated valve that allows manual operation of the system if the pressure source is inoperative. Due at least in part to the incorporation of the relief valve assembly into the system, the metering element is coupled to the control valve assembly such that the metering element is rotated manually by the control valve assembly so as to act as a pump in the event of pressure source failure.
In accordance with another aspect of the invention, a method of steering a watercraft includes placing a pressure source in fluid communication with a high pressure port of a helm casing of a helm and a first chamber in a hydraulic steering cylinder located remote from the helm casing, the first chamber being separated from a second chamber by a steering piston, and a driven member being formed by one of the steering cylinder and the rod and being coupled to a steered mechanism of the watercraft. Then, in response to movement of a steering mechanism of the watercraft in a first direction from an at-rest position thereof, the system causes a metering element in the helm casing to rotate in a first direction and deliver fluid to the second chamber in the steering cylinder, thereby causing the driven member to move in a first direction. Conversely, in response to movement of the steering mechanism in a second direction from the neutral position, the system causes the metering element to rotate in a second direction to permit hydraulic fluid to flow into the metering element from the second chamber in the steering cylinder, thereby causing the driven member to move in a second direction opposite the first direction.
In a preferred embodiment, the metering element has a first port and has a second port in fluid communication with the second chamber in the steering cylinder. In this system, when the steering mechanism is in the at-rest position, a control valve assembly of the helm is switched to a first state isolating the first port of the metering element from the pressure source and from vent. When the steering mechanism moves in the first direction from the at-rest position, the control valve assembly switches to a second state fluidically coupling the first port in the metering element to the pressure source. Conversely, when the steering mechanism moves in the second direction, the valve assembly switches to a third position fluidically coupling the first port in the metering element to vent.
In order to facilitate mounting of the helm to the dash of the watercraft, the helm has only three ports (namely, a slave port that is fluidically connected to the second chamber in the steering cylinder, the high pressure port, and the return port), and all three ports are all located on a rear axial end of the helm cylinder. The helm cylinder also is very compact.